A conventional adjustable wrench generally includes a handle with a fixed jaw integrally connected to an end thereof and a movable jaw which is movable relative to the fixed jaw so as to clamp an object by the fixed jaw and the movable jaw. Generally, the size of the object clamped by the wrench cannot be told, the user has to use another measurement tool to measure the object before it is rotated by the wrench. A wrench that is developed to have scale markings pressed in a side of the wrench so that the user may check the markings to know the size of the object. Nevertheless, it requires a certain experience to identify the correct scale markings. In other words, there is an error could potentially occur when reading the scale markings if the user views the scale markings at an angle. Besides, the scales are pressed in the surface of the wrench and will be worn out after the wrench is used for a period of time.
The present invention intends to provide a wrench that has a display device which transfers changes of resistance of a variable electric resistor when clamping the object to display the correct size in the screen of the display device.